linux-kernel - Re: [PATCH v17 10/33] fs/resctrl: Introduce the interface to display monitoring modes

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Message-ID: <accea3ea-88b9-40d1-8a66-86d29d68c69a@intel.com>
Date: Tue, 2 Sep 2025 19:30:15 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <corbet@....net>, <tony.luck@...el.com>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>
CC: <Dave.Martin@....com>, <james.morse@....com>, <x86@...nel.org>,
	<hpa@...or.com>, <akpm@...ux-foundation.org>, <rostedt@...dmis.org>,
	<paulmck@...nel.org>, <pawan.kumar.gupta@...ux.intel.com>, <kees@...nel.org>,
	<arnd@...db.de>, <fvdl@...gle.com>, <seanjc@...gle.com>,
	<thomas.lendacky@....com>, <yosry.ahmed@...ux.dev>, <xin@...or.com>,
	<sohil.mehta@...el.com>, <kai.huang@...el.com>, <xiaoyao.li@...el.com>,
	<peterz@...radead.org>, <mario.limonciello@....com>, <xin3.li@...el.com>,
	<perry.yuan@....com>, <chang.seok.bae@...el.com>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<peternewman@...gle.com>, <eranian@...gle.com>, <gautham.shenoy@....com>
Subject: Re: [PATCH v17 10/33] fs/resctrl: Introduce the interface to display
 monitoring modes

Hi Babu,

On 8/14/25 7:25 PM, Babu Moger wrote:
> Introduce the resctrl file "mbm_assign_mode" to list the supported counter
> assignment modes.
> 
> The "mbm_event" counter assignment mode allows users to assign a hardware
> counter to an RMID, event pair and monitor bandwidth usage as long as it is
> assigned. The hardware continues to track the assigned counter until it is
> explicitly unassigned by the user. Each event within a resctrl group can be
> assigned independently in this mode.
> 
> On AMD systems "mbm_event" mode is backed by the ABMC (Assignable
> Bandwidth Monitoring Counters) hardware feature and is enabled by default.
> 
> The "default" mode is the existing mode that works without the explicit
> counter assignment, instead relying on dynamic counter assignment by
> hardware that may result in hardware not dedicating a counter resulting
> in monitoring data reads returning "Unavailable".
> 
> Provide an interface to display the monitor modes on the system.
> 
> $ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
> [mbm_event]
> default
> 
> Add IS_ENABLED(CONFIG_RESCTRL_ASSIGN_FIXED) check to support Arm64.
> 
> On x86, CONFIG_RESCTRL_ASSIGN_FIXED is not defined. On Arm64, it will be
> defined when the "mbm_event" mode is supported.
> 
> Add IS_ENABLED(CONFIG_RESCTRL_ASSIGN_FIXED) check early to ensure the user
> interface remains compatible with upcoming Arm64 support. IS_ENABLED()
> safely evaluates to 0 when the configuration is not defined.
> 
> As a result, for MPAM, the display would be either:
> [default]
> or
> [mbm_event]
> 
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---
Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>

Reinette